1. Field of the Invention
The present invention relates to a disk drive device that rotationally drives a disk.
2. Description of the Related Art
In recent years, disk drive devices such as HDDs (Hard disk drives) have been dramatically improved in rotational accuracy by being provided with fluid dynamic bearings, and therefore those with high density and large capacity can be available. Due to this, disk drive devices provided with fluid dynamic bearings have been mounted in a wide variety of apparatuses. Accordingly, the disk drive devices have been used in various environments.
For example, a spindle motor is disclosed in Japanese Patent Application Publication No. 2002-266852, in which a first taper surface having a taper angle of θ1 is formed on the outer circumferential surface of a shaft and a second taper surface having a taper angle of θ2 is formed on the inner circumferential surface of a sleeve, and the taper angles θ1 and θ2 have a relationship of θ1>θ2.
It is demanded that a disk drive device exhibits high reliability even if the shaft thereof is maintained in a horizontal state in order to enhance freedom in the arrangement of the disk drive device. That is, a disk drive device having the following characteristics is demanded, namely, even if an impact is applied to a disk drive device when the shaft thereof is maintained in a horizontal state: the disk drive device is stable; read/write of magnetic data can be normally performed; and the lifetime of the disk drive device will not be shortened.
There is a phenomenon in which, if a disk drive device provided with a fluid dynamic bearing unit is used when the shaft thereof is maintained in a horizontal state, the lifetime of the disk drive device will be shortened in comparison with the case where a disk drive device provided with the same fluid dynamic bearing unit is used when the shaft thereof is maintained in a vertical state. In particular, the lifetime of a disk drive device will be sometimes significantly shortened if an impact is applied thereto when the shaft thereof is maintained in a horizontal state. Accordingly, the present inventor has acquired the following knowledge after studying on the mechanism by which these phenomena occur.
When the amount of the lubricant in a fluid dynamic bearing unit is decreased, the function as a bearing is deteriorated and the rotation of the fluid dynamic bearing unit becomes unstable. When operations of reading/writing magnetic data are not performed normally, the lifetime of the disk drive device will be shortened. If a disk drive device is used when the shaft thereof is maintained in a horizontal state, the gas-liquid interface of the lubricant is tilted due to gravity. If the tilt angle of the gas-liquid interface of the lubricant is large, the contact area of the lubricant with air is increased and the amount of the lubricant is decreased at a rapid pace due to evaporation, thereby the lifetime thereof being shortened.
In addition, part of the tilted lubricant is to be closer to the opening of a fluid dynamic bearing unit, causing the fear that the lubricant may be dispersed outside the fluid dynamic bearing unit even when a small impact is applied thereto. When the amount of lubricant is decreased after the lubricant has been dispersed outside a fluid dynamic bearing unit, the lifetime of the fluid dynamic bearing will be shortened.